The present invention pertains to an implantable medical system, and to an associated methodology, employing, and managed by electrical circuit structure, which features logic-including, internal-control circuitry referred to herein as computer structure, or more simply as a computer, for enhancing hemodynamic performance in subjects with cardiac disease through applying carefully timed, regular, per-cardiac-cycle, synchronized, asymptomatic, electrical pulsed stimulation to the diaphragm intended to induce short-term occurrences of biphasic diaphragmatic motion. In particular, it relates to such a system and methodology which, in relation to each such stimulation, and through operation of the included control circuitry (which forms part of what is referred to as electrical circuit structure), monitors and records information regarding resulting, induced diaphragmatic-motion for later review, and to accommodate potential, telemetry-adjusted, systemic-performance adaptation to improve diaphragmatic stimulation characteristics so as to maximize the sought hemodynamic-performance enhancement. The system preferably additionally permits, in a modified form, selective, remote-telemetry-implemented communication from outside the anatomy to allow for other kinds of system-behavioral adjustments, such as ones that relate to timing matters.
The term “hemodynamic performance” is used synonymously herein with the terms “cardiovascular performance” and “cardiac function”. The biphasic diaphragmatic motion produced by electrical stimulation, in accordance with practice of the invention, is what is called herein caudal-followed-by-cranial motion of the diaphragm. The included “computer-structure” logic componentry, which may be hard-wired to perform its intended functions, or more preferably fully or partially programmable, as by telemetry, may also feature an appropriate microprocessor. It may also include, or be appropriately internally associated with, a suitable “state machine” for implementing various important timing controls, as will be explained below.
Pulsed stimulation of the type just above mentioned, properly characterized and applied, triggers, in each case, a very short (only a few tens of milliseconds) pulse-like, biphasic (singular-caudal-followed-by-singular-cranial) motion of the diaphragm, and, relatedly also, a substantially following pumping-relevant motion of the left ventricle in the heart which rests on the diaphragm. This stimulation creates this motion-generating activity in a manner which, when properly and synchronously timed in relation to the onset of left-ventricular contraction, improves hemodynamic performance through enhancing the important cardiac pumping functions of both (a) late diastolic filling, and (b) early systolic contraction.
Asymptomatic stimulation implemented in the practice of the present invention is also referred to herein as PIDS stimulation—the acronym PIDS standing for the phrase “pacing induced diaphragmatic stimulation”. The mentioned monitoring and recording for later stimulation-characteristic review, and possible revision purposes, are linked with systemically control-circuitry-performed comparing of actual induced diaphragmatic-motion waveforms with a provided and internally stored reference waveform.
Of key importance in all featural expressions of the present invention, systemic and methodologic, are (1) that sensing of what is referred to herein as a valid electrical or mechanical V-event, and (2) that related, sensing-based, ultimate applying of electrical stimulation to the diaphragm, take place, with the system installed for use with a subject, from an implanted systemic disposition directly adjacent, and preferably in contact with, a selected surface region in the subject's diaphragm. Preferably, but not necessarily, this selected surface region, which may be either an inferior (preferred), or a superior, surface region in the diaphragm, and which may be chosen to be at many different, diaphragmatic surface locations, is disposed left-lateral relative to the subject's anatomy—and under all circumstances, out of contact with the heart.
A V-event, in either category (electrical or mechanical), is defined herein as being either the onset of left-ventricular contraction, or a cardiac electrical or mechanical event having a predictably known relationship to such an onset. A valid electrical V-event is treated as being either the electrical R or Q wave, and a valid mechanical V-event is treated as being the S1 heart sound. Cardiac-cycle-by-cardiac-cycle, synchronized, diaphragmatic stimulation is timed, selectively in different ways—anticipatory (early), or following (late)—in relation to per-cardiac-cycle, detected, valid V-events.
Of special importance in certain featural expressions of the present invention, systemic and methodologic, is the effective incorporation in the proposed system and associated methodology of a focus, through the use of a system-included accelerometer, preferably multi-axial in character, and even more preferably three-dimensional in nature, on the monitoring and recording of the mechanical waveform of per-cardiac-cycle, mechanical diaphragmatic biphasic motion which is actually produced by applied, electrical diaphragmatic stimulation in comparison with a pre-set, diaphragmatic-motion reference waveform. Information regarding non-conformance of these two waveforms—computer acquired and recorded according to the invention—is important for periodic system-performance review, and in this context, is very useful to support the making, when desired, of appropriate, per-cardiac-cycle, electrical stimulation-character modifications to enhance such performance.
It should be noted that while different embodiments of the invention may use different-axial-sensitivity accelerometers, preferred in most applications is the inclusion and use of a three-dimensional, i.e., three-axis, accelerometer. Accordingly, the preferred systemic and methodologic invention descriptions presented hereinbelow are described in the context of employment of a three-dimensional accelerometer.
Two, principal, implantable systemic forms, or embodiments, of the invention are proposed, one of which features, as an entirety—i.e., as a singularity—a self-contained, self-powered, singular capsule construction, and the other of which features a distribution, also self-powered, of components organized into two arrangements of components separated by an interconnecting, cross-communication lead structure.
Other forms of the invention, not pictured or discussed herein, and differing specifically from the two, just-mentioned currently principal, preferred forms, are recognized to be very suitably possible to address different implantation applications, wherein the various system components, described below for the two invention forms particularly set forth herein, become organized in different implantable ways.
Regarding systemic performance functionality in the context of the present invention disclosure, the same, basic invention methodology, in terms of the important, end-result achieving of hemodynamic/cardiovascular performance enhancement through triggered pulses of biphasic motion introduced into the diaphragm (as above outlined), is implemented in both of the specifically herein described systemic invention forms.
Stimulation-induced diaphragmatic movements, as just generally described above, are, in relation to normal respiration-motion frequency (typically about 0.2-0.3-Hz), and as mentioned, short-term, relatively high-frequency (typically about 12-15-Hz), pulse-like motions. These quick motions are superimposed on the regular, and much lower frequency, diaphragmatic respiration movements. The initial, short-term caudal movement effected by diaphragmatic stimulation pulls on the left ventricle, and if well timed, such stimulation-resulting “pulling” increases the atrial contribution to left-ventricular filling during late diastole (i.e., a so-called “atrial kick”) with a resulting subsequent increase in stroke volume via the recognized, Frank-Starling mechanism. The secondary, stimulation-induced movement of the diaphragm which is cranial, and which is also much faster than regular diaphragmatic respiratory motion, causes the left ventricle to be “kicked” upwardly, and If this secondary movement occurs in the early part of systole, and prior to the closure of the mitral valve, it enhances cardiac function further by increasing the momentum of ventricular contraction.
Accordingly, in relation to achieving desired hemodynamic-enhancement, it is important to optimize the timing between the onset of ventricular contraction and diaphragmatic stimulation so that the actual timing and impact of the mentioned caudal and cranial components of motion as they affect cardiac function are maximized. Such maximizing is subject-specific, in relation, of course, to a given subject's particular cardiac structure (electrically and mechanically), and accordingly, medically-determined, properly associated, subject-specific timing requirements are initially “set into the system of the invention”, as will be explained. When all operational parameters are properly “put in place”, the present invention successfully accomplishes appreciable hemodynamic-performance optimization.
As mentioned above, two, fully implantable, and fully self-powered, principal embodiments of the system of the present invention are specifically illustrated and described herein, one of which, as stated above, is a single-unit, self-contained, capsule-form arrangement, and the other of which has a distributed-component, communication-lead-line-interconnecting form.
According to one manner of describing generally the structural nature of the present invention, what is proposed is a system including (a) bi-modal (cardiac-electrical-activity sensing in one mode, and related diaphragmatic electrical stimulating in the other mode) electrode structure operatively connectable to a selected surface region in a subject's diaphragm, and (b) monitoring and controlling circuit structure which is connected to the electrode structure, and operable (1) to receive and process electrode-structure-sensed electrical cardiac activity when the electrode structure, under the influence of the circuit structure, is functioning in its sensing mode, and (2), based on such receiving and processing, to communicate to the diaphragm via the electrode structure, when the latter is functioning, also under the influence of the circuit structure, in its stimulating mode, appropriate diaphragmatic stimulation.
In a more particular sense respecting this just-above-presented systemic expression of the invention, (a) the selected, diaphragmatic surface region is disposed (1) preferably, but not necessarily, at a location which is lateral, and even more specifically left-lateral, within a subject's anatomy, and (2) in all instances out of contact with, the subject's heart, and (b) the mentioned circuit structure includes computer structure which specifically operates, relative to the circuit structure's delivery of electrical stimulation through the electrode structure, to control appropriately predetermined timed relationships relative to noted presences, in received and monitored cardiac-cycle electrical-activity information, of valid electrical V-events. Additionally, contemplated in the practice of the invention are two, different categories of such predetermined timed, or timing, relationships, one of which involves anticipation of a next-expected, valid, cardiac-cycle, electrical V-event, and the other of which involves a following of the last-sensed, valid, cardiac-cycle, electrical V-event. These same, two categories of timing relationships are equally applicable to another form of the system of the invention, discussed below, which further includes an accelerometer (single or plural-axis), also referred to herein as a mechanical sensing structure, that is designed to detect heart sounds, and in particular S1 heart sounds, as valid mechanical V-events.
An augmented form (the “another form” of the invention mentioned immediately above) of this just-presented description of the invention is one in which the proposed system further includes specifically a three-dimensional accelerometer (called also a mechanical sensing structure), (a) disposed adjacent, and operatively associated with, the electrode structure for contact-associated disposition in a motion-sensing relationship with, and with respect to, the subject's diaphragm, (b) operatively connected to the mentioned circuit structure, and (c) constructed to be responsive to any motion produced in the subject's diaphragm as a consequence of electrical diaphragmatic stimulation, and in relation to such responsiveness, to generate and communicate to the circuit structure a diaphragmatic-motion confirmation signal possessing a waveform which is directly indicative of such motion.
In a further way of thinking about the accelerometer-including system form of the invention, the circuit structure's included computer structure features a waveform monitoring and recording substructure for comparing the waveform of a communicated confirmation signal with a reference waveform, and recording the conformation-signal waveform for subsequent review.
Another way of thinking about the invention, in relation to the inclusion therein of an accelerometer, is that, in accordance with a modified form of the invention, (a) an included accelerometer functions, additionally, for sensing, in a subject's cardiac cycles, cardiac-cycle, S1 heart-sound, mechanical activity—a valid mechanical V-event—which is discernible at the selected, diaphragmatic surface region, and that (b), the included circuit structure receives this mechanical valid V-event information from the accelerometer, and is operable, in predetermined timed relationships to noted presences, in such received mechanical S1-heart-sound, of valid V-event information, to deliver asymptomatic electrical stimulation through the electrode structure to the subject's diaphragm for the purpose of triggering the intended biphasic, caudal-followed-by-cranial, motion of the diaphragm.
A further modified form of the basic system of the invention, contemplated for implementation in certain applications, and representationally pictured, described and included herein in each of the two principal embodiments disclosed, is one wherein the computer structure which forms part of the included circuit structure possesses timing-adjustment substructure capable of making an adjustment periodically in the predetermined timed relationship which determines when, in relation to a sensed, valid V-event, electrical diaphragmatic stimulation occurs. This modification is versatile in its utility, offering the possibility of adjusting, either remotely, or internally automatically if desired, such stimulation timing in a manner aimed at further enhancing a subject's hemodynamic performance if, and as, the subject's heart-behavior conditions change over time.
These and other systemic aspects of the invention, preferred and modified, are discussed below herein.
From a methodologic point of view the invention offers a method for improving the hemodynamic performance of a subject's heart including, from adjacent a selected surface region in the subject's diaphragm which is out of contact with, the heart, (1) sensing and noting the presences in the subject's cardiac cycles of a selected one of (a) per-cycle valid electrical, and (b) per-cycle valid mechanical, V-events, (2) based upon such sensing, and upon noting each of such selected, V-event presences, applying, in a predetermined timed relationship to such a noting, associated, asymptomatic electrical stimulation directly to the diaphragm, preferably at the selected diaphragmatic surface region, for the purpose of triggering biphasic, caudal-followed-by-cranial motion of the diaphragm, (3) following the applying step, monitoring the waveform of resulting diaphragmatic motion, (4) after performing the monitoring step, comparing the monitored diaphragmatic-motion waveform with a reference, diaphragmatic-motion waveform, and (5) on completion of the comparing step, recording the monitored, diaphragmatic-motion waveform for later review.
The invention methodology further includes (1) choosing the selected diaphragmatic surface region to be on one of (a) the inferior, and (b) the superior, side of the diaphragm, and (2) choosing the selected, per-cycle valid V-event whereby, if it is to be electrical, it is one of (a) the R wave, and (b) the Q wave, and if mechanical, it is the S1 heart sound.
These and various other features and advantages that are offered by the system and methodology of the present invention will become more fully apparent as the detailed description of the invention which follows below is read in conjunction with the accompanying drawings.